Multiple frequency band operation in wireless networks

ABSTRACT

Embodiments for bandwidth allocation methods, detecting interference with other systems, and/or redeploying in alternate bandwidth are described. Higher bandwidth channels may be deployed at channel boundaries ( 410 ), which are a subset of those for lower bandwidth channels ( 310 ), and may be restricted from overlapping. Interference may be detected ( 930 ) on primary, secondary, or a combination of channels, and may be detected in response to energy measurements ( 910 ) of the various channels. When interference is detected, a higher bandwidth Basic Service Set (BSS)( 100 ) may be relocated to an alternate channel, or may have its bandwidth reduced to avoid interference. Interference may be detected based on energy measured on the primary or secondary channel, and/or a difference between the two. An FFT ( 1010 ) may be used in energy measurement in either or both of the primary and secondary channels. Stations may also monitor messages from alternate systems to make channel allocation decisions. Various other aspects are also presented.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent is a Divisional and claims priorityto patent application Ser. No. 11/253,358 entitled “Multiple FrequencyBand Operation In Wireless Networks” filed Oct. 18, 2005, andProvisional Application No. 60/620,488 entitled “Method and Apparatusfor Multiple Frequency Band Operation In Wireless Networks” filed Oct.20, 2004, assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

BACKGROUND

1. Field

The present disclosure relates generally to wireless communications, andamongst other things to multiple frequency band operation.

2. Background

Wireless communication systems are widely deployed to provide varioustypes of communication such as voice and data A typical wireless datasystem, or network, provides multiple users access to one or more sharedresources. A system may use a variety of multiple access techniques suchas Frequency Division Multiplexing (FDM), Time Division Multiplexing(TDM), Code Division Multiplexing (CDM), and others.

Example wireless networks include cellular-based data systems. Thefollowing are several such examples: (1) the “TIA/EIA-95-B MobileStation-Base Station Compatibility Standard for Dual-Mode WidebandSpread Spectrum Cellular System” (the IS-95 standard), (2) the standardoffered by a consortium named “3rd Generation Partnership Project”(3GPP) and embodied in a set of documents including Document Nos. 3G TS25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMAstandard), (3) the standard offered by a consortium named “3rdGeneration Partnership Project 2” (3GPP2) and embodied in “TR-45.5Physical Layer Standard for cdma2000 Spread Spectrum Systems” (theIS-2000 standard), and (4) the high data rate (HDR) system that conformsto the TIA/EIA/IS-856 standard (the IS-856 standard).

Other examples of wireless systems include Wireless Local Area Networks(WLANs) such as the IEEE 802.11 standards (i.e. 802.11 (a), (b), or(g)). Improvements over these networks may be achieved in deploying aMultiple Input Multiple Output (MIMO) WLAN comprising OrthogonalFrequency Division Multiplexing (OFDM) modulation techniques. IEEE802.11(e) has been introduced to improve upon some of the shortcomingsof previous 802.11 standards.

Networks such as the 802.11 networks operate using one of severalpre-defined channels within unlicensed spectrum. Alternate networks maybe deployed within the same spectrum that achieve higher throughput byusing higher bandwidth channels. A network may use a frequencyallocation that comprises one or more of legacy pre-defined channels.Such networks, if deployed in the same spectrum as legacy systems, mayneed to avoid interference with or interoperate with legacy systems. Itis desirable to deploy networks so as to more efficiently use theavailable spectrum. There is therefore a need in the art for bandwidthallocation methods for efficient use of the shared spectrum, fordetecting interference or collisions with other systems, and/orredeploying in alternate bandwidth when interference is detected.

SUMMARY

Embodiments disclosed herein address the need in the art for multiplefrequency band operation in wireless networks.

In several aspects, an apparatus comprises a memory and a processorcoupled with the memory. The processor configured to select a channelfor establishing at a selected channel bandwidth from at least a firstchannel bandwidth and a second channel bandwidth and a selected channelboundary from a plurality of first channel boundaries when the firstchannel bandwidth is selected and from a plurality of second channelboundaries when the second channel bandwidth is selected, wherein thesecond channel boundaries are a subset of the first channel boundariesand each of the plurality of second channel boundaries are separatedfrom the remainder of the plurality of second channel boundaries by atleast the second channel bandwidth.

In additional aspects, a Carrier Sense Multiple Access/CollisionAvoidance system that supports transmission on a shared channelcomprising at least a primary channel and a secondary channel includes amethod comprising measuring energy of the primary channel, measuringenergy of the secondary channel, and determining interference inaccordance with the measured energy of the primary channel and themeasured energy of the secondary channel.

In further aspects, a Carrier Sense Multiple Access/Collision Avoidancesystem that supports transmission on a shared channel comprising atleast a primary channel and a secondary channel includes a methodcomprising detecting interference on the primary or secondary channel ofa first shared channel, reducing the bandwidth of the first sharedchannel to the bandwidth of the primary channel when interference isdetected on the secondary channel, and reducing the bandwidth of thefirst shared channel to the bandwidth of the secondary channel wheninterference is detected on the primary channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general block diagram of a wireless communication systemcapable of supporting a number of users.

FIG. 2 depicts aspects of a plurality of BSSs located near each other;

FIG. 3 depicts an example allocation of channels for a system such aslegacy 802.11;

FIG. 4 depicts an example allocation of contiguous high throughputchannels located at a subset of legacy channel boundaries;

FIG. 5 depicts an example scenario of several established BSSs;

FIG. 6 depicts aspects of a wireless communication device;

FIG. 7 depicts aspects of a method for establishing a higher bandwidthchannel at one of a subset of lower bandwidth channel boundaries;

FIG. 8 depicts aspects of a method for monitoring established channels,measuring interference, and reporting those measurements;

FIG. 9 depicts aspects of a portion of a wireless communication deviceused for monitoring an established BSS;

FIG. 10 depicts aspects of multiple frequency band energy measurementblock;

FIG. 11 depicts aspects of a method for modifying a BSS in response tomeasured interference;

FIG. 12 depicts aspects of a method for determining if interference isoccurring on a multiple frequency band wireless network; and

FIG. 13 depicts aspects of a method 1300 for responding to BSSmodification messages from an alternate BSS.

DETAILED DESCRIPTION

Various aspects will be detailed below, one or more of which may becombined in any given embodiment. In aspects, a system is deployed tooperate in one of two carrier modes: 20 or 40 MHz. Various otherembodiments may use alternate parameters for the bandwidth selection,and may use more than two frequency bands to form wider channels andachieve higher throughput. This aspects is designed to interoperateefficiently with legacy 802.11 systems, which operate on one of aplurality of 20 MHz channels. As used herein, the term “high throughput”or “HT” may be used to distinguish systems or stations (STAs) operatingin accordance with a next generation standard, such as a multiplefrequency band system described herein. The term “legacy” may be used toidentify other systems with which interference is to be avoided. Thoseof skill in the art will recognize that other systems besides legacysystems may also operate within the spectrum of interest, and it will beclear that the aspects described herein are compatible with such systemsas well. In this example, a selection of enabling features for simpleand effective 20/40 MHz operation are as follows.

In one aspect, 40 MHz carriers comprise even-odd pairs of carriers. Thus20 MHz carriers are paired as follows: (2 n, 2 n+1), where n is chosento select two contiguous legacy carriers. A 40 MHz Basic Service Set(BSS), in this embodiment, does not pair two 20 MHz carriers of the form(2 n+1, 2 n+2). This ensures that, in these aspects, overlapping 40 MHzBSS (if they exist) have the same primary (2 n) and secondary (2 n+1)carriers. The allocation efficiency of this aspect is detailed furtherbelow.

In another aspect, procedures may be designed to disallow theestablishment of a 40 MHz BSS overlapping with different 20 MHz BSSs onthe two 20 MHz carriers. Because medium access procedures to coordinatemedium access activity across the two 20 MHz carriers to enable 40 MHzoperation may be undesirably complicated and wasteful, when thissituation arises, the 40 MHz BSS falls back to 20 MHz. In alternateembodiments, this limitation need not be introduced.

In another aspect, in an example BSS with mixed 40 MHz and 20 MHz (HT orlegacy) STAs, medium access is managed on the primary carrier (2 n). For40 MHz transmissions, Clear Channel Assessment (CCA) may be performed onthe secondary carrier (2 n+1). In one embodiment, when the shared mediumis detected to be busy on the secondary carrier, the STA only transmitson the primary carrier.

In another aspect, monitoring of the secondary carrier is performed. Forexample, during reception of 20 MHz transmissions, as well as duringback-off, STAs may perform CCA on the secondary carrier. Signal to NoiseRatio (SNR) degradation and/or other interference events on thesecondary carrier may be determined and reported. Examples of suchmonitoring are detailed further below.

Various other aspects and embodiments are also described below.

Aspects are disclosed herein that support, among other aspects, highlyefficient operation in conjunction with very high bit rate physicallayers for a wireless LAN (or similar applications that use newlyemerging transmission technologies). The example WLAN is operable in twofrequency band modes, 20 MHz and 40 MHz. It supports bit rates in excessof 100 Mbps (million bits per second) including up to 300 Mbps inbandwidths of 20 MHz, and up to 600 Mbps in bandwidths of 40 MHz.Various alternate WLANs are also supported, including those with morethan two frequency band modes, and any number of supported bit rates.

Various aspects preserve the simplicity and robustness of thedistributed coordination operation of legacy WLAN systems, examples ofwhich are found in 802.11 (a-e). The advantages of the variousembodiments may be achieved while maintaining backward compatibilitywith such legacy systems. (Note that, in the description below, 802.11systems may be described as example legacy systems. Those of skill inthe art will recognize that the improvements are also compatible withalternate systems and standards.)

For 802.11n, backward compatible PPDU types are introduced. In aspects,extended SIGNAL fields are introduced in the legacy PLCP Header to bebackward compatible with the SIGNAL field of legacy 802.11. Unusedvalues of the RATE field in the legacy SIGNAL field are set to definenew PPDU types. Other schemes may be used to indicate the presence ofnew PPDU types. This example high throughput system is disclosed inrelated co-pending U.S. patent application Ser. No. 10/964,330, entitled“HIGH SPEED MEDIA ACCESS CONTROL WITH LEGACY SYSTEM INTEROPERABILITY”,filed Oct. 13, 2004, assigned to the assignee of the present disclosureand incorporated by reference herein (hereinafter the '330 application).

In the '330 application, several new PPDU types are introduced. Forbackward compatibility with legacy STAs, the RATE field in the SIGNALfield of the PLCP Header is modified to a RATE/Type field. Unused valuesof RATE are designated as PPDU Type. The PPDU Type also indicates thepresence and length of a SIGNAL field extension designated SIGNAL2.Other schemes may be used to indicate the presence and length of theSIGNAL field extension. The preamble, SIGNAL field, SIGNAL fieldextension and additional training are referred to as the extendedpreamble.

In aspects, during 40 MHz transmissions, the extended preamble includinglegacy preamble, legacy SIGNAL field and the HT SIGNAL field (i.e.SIGNAL2) and training are transmitted on both the primary and secondarycarriers.

One or more exemplary embodiments described herein are set forth in thecontext of a wireless data communication system. While use within thiscontext is advantageous, different embodiments of the disclosure may beincorporated in different environments or configurations. In general,the various systems described herein may be formed usingsoftware-controlled processors, integrated circuits, or discrete logic.The data, instructions, commands, information, signals, symbols, andchips that may be referenced throughout the application areadvantageously represented by voltages, currents, electromagnetic waves,magnetic fields or particles, optical fields or particles, or acombination thereof. In addition, the blocks shown in each block diagrammay represent hardware or method steps. Method steps can be interchangedwithout departing from the scope of the present disclosure. The word“exemplary” is used herein to mean “serving as an example, instance, orillustration.” Any embodiment described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otherembodiments.

FIG. 1 illustrates exemplary embodiments of system 100, comprising anAccess Point (AP) 104 connected to one or more User Terminals (UTs)106A-N. In accordance with 802.11 terminology, in this document the APand the UTs are also referred to as stations or STAs. The techniques andembodiments described herein are also applicable to other types ofsystems (examples include the cellular standards detailed above). Asused herein, the term base station can be used interchangeably with theterm access point. The term user terminal can be used interchangeablywith the terms user equipment (UE), subscriber unit, subscriber station,access terminal, remote terminal, mobile station, or other correspondingterms known in the art. The term mobile station encompasses fixedwireless applications.

Note also that user terminals 106 may communicate directly with oneanother. The Direct Link Protocol (DLP), introduced by 802.11(e), allowsa STA to forward frames directly to another destination STA within aBasic Service Set (BSS) (controlled by the same AP). In variousembodiments, as known in the art, an access point is not required. Forexample, an Independent BSS (IBSS) may be formed with any combination ofSTAs. Ad hoc networks of user terminals may be formed which communicatewith each other via wireless network 120 using any of the myriadcommunication formats known in the art.

The AP and the UTs communicate via Wireless Local Area Network (WLAN)120. In the aspects, WLAN 120 is a high speed MIMO OFDM system. However,WLAN 120 may be any wireless LAN. Optionally, access point 104communicates with any number of external devices or processes vianetwork 102. Network 102 may be the Internet, an intranet, or any otherwired, wireless, or optical network. Connection 110 carries the physicallayer signals from the network to the access point 104. Devices orprocesses may be connected to network 102 or as UTs (or via connectionstherewith) on WLAN 120. Examples of devices that may be connected toeither network 102 or WLAN 120 include phones, Personal DigitalAssistants (PDAs), computers of various types (laptops, personalcomputers, workstations, terminals of any type), video devices such ascameras, camcorders, webcams, and virtually any other type of datadevice. Processes may include voice, video, data communications, etc.Various data streams may have varying transmission requirements, whichmay be accommodated by using varying Quality of Service (QoS)techniques.

System 100 may be deployed with a centralized AP 104. All UTs 106communicate with the AP in one aspects. In an alternate embodiment,direct peer-to-peer communication between two UTs may be accommodated,with modifications to the system, as will be apparent to those of skillin the art, examples of which are illustrated below. Any station may beset up as a designated AP in embodiments supporting designated accesspoints. Access may be managed by an AP, or ad hoc (i.e. contentionbased).

In one embodiment, AP 104 provides Ethernet adaptation. In this case, anIP router may be deployed in addition to the AP to provide connection tonetwork 102 (details not shown). Ethernet frames may be transferredbetween the router and the UTs 106 over the WLAN sub-network (detailedbelow). Ethernet adaptation and connectivity are well known in the art.

In an alternate embodiment, the AP 104 provides IP Adaptation. In thiscase, the AP acts as a gateway router for the set of connected UTs(details not shown). In this case, IP datagrams may be routed by the AP104 to and from the UTs 106. IP adaptation and connectivity are wellknown in the art.

FIG. 2 depicts aspects of a plurality 200 of BSSs 100A-100D. In thisexample, each BSS is located geographically near each other, withinterference indicated by overlapping circles. Thus, BSS 100A does notinterfere with BSS 100C or 100D. BSS 100B is shown to interfere slightlyat the perimeter of BSS 100C, but interferes almost entirely with BSS100A. In the aspects, unlicensed spectrum is used to deploy variouscommunication systems, such as legacy or high throughput 802.11 systems,described above. Thus, when establishing a new BSS, an access point (orany other device establishing a BSS) may select from any availablechannel supported by its communication protocol. However, to utilizespectrum more efficiently, BSSs may be established according to variousrules, or following other procedures, to minimize the effects ofinterference with each other. Various aspects described hereinillustrate methods for avoiding establishing a BSS in an interferinglocation, detecting when interference is generated, moving, from onechannel to another upon interference detection, and backing off from ahigher bandwidth channel to a lower bandwidth channel to avoidinterference, among others. As noted above, a given embodiment maycomprise any combination of one or more of the aspects described herein.

FIG. 3 depicts an example allocation of channels for a system such as alegacy 802.11 system, known in the prior art. This channel allocationscheme may be used to deploy a plurality of BSSs 200, such as thatdescribed above in FIG. 2. In this example, 20 MHz channels 320A-N areidentified contiguously, and assigned the names channel 0 throughchannel N-1. The channels 320 are separated at channel boundaries310A-N, respectively. In a legacy 802.11 example, there are 12 channels,0-11. Each channel 320 has a channel boundary 310 identifying the startof that bandwidth allocation. In aspects, these channel boundaries 310have been defined in the 802.11 specification.

In one embodiment, in order to occupy spectrum shared among multiplehigh throughput BSSs in a more efficient manner, the channels areallocated contiguously, as depicted in FIG. 4. In this example, thehigher bandwidth channels are allocated 40 MHz, or twice that of alegacy 802.11 channel. In alternate embodiments, other channelboundaries may be used. In this example, the 40 MHz channel boundaries410A-N indicate the allowable channel boundaries for 40 MHz channels420A-N, labeled channel 0-(M-1). In this example, the channel boundaries420 are selected as a subset of the channel boundaries 310.

In an unlicensed spectrum, it may not be possible to mandate that alldevices operating therein follow any given set of rules, such as legacy802.11, high throughput techniques as described above, or as describedin the various embodiments detailed herein. However, to the extent thatwireless communication devices establish each BSS in accordance withthese techniques, the bandwidth may be utilized more efficiently. Inthis embodiment, the 40 MHz channel boundaries supported are contiguous40 MHz channels aligned at a subset of the 20 MHz boundaries defined for802.11. In various embodiments described herein, this aspect may beassumed. However, this contiguous channel allocation, while oftenbeneficial, is not a requirement of embodiments including various otheraspects. For example, high throughput channels may be allowed toestablish at channel boundaries that potentially overlap with other highthroughput channels, and channels are not mandated to be contiguous.Those of skill in the art will recognize when to deploy systemsaccording to this aspect when making tradeoffs between flexibility andoptimization of the shared resource.

FIG. 5 depicts an example scenario of several established BSSs. In thisexample, BSS1 100A is established on 40 MHz channel 0 (or 420A, usingthe channel boundary definitions of FIG. 4). A BSS2 100B is establishedat the channel boundary adjacent to 100A. In this example, BSS2 is shownoperating in 20 MHz. This may be a high throughput system operating in a20 MHz mode, or may be a legacy 802.11 BSS, or any other BSS operatingin less than 40 MHz channel width available at channel boundary 420B.For illustration, assume that a new BSS, BSS3 100C, is to be establishedrequiring a 40 MHz channel allocation. Using various techniques detailedfurther below, BSS3 will be established at another 40 MHz channelboundary, possibly the next higher 40 MHz channel boundary 410, asshown. In this example, the bandwidth channel boundary is selected inorder to avoid interference with any of the existing BSSs, whetherlegacy or HT.

Also note, as shown in FIG. 5, that BSS5 100E is shown operating in theupper 20 MHz band adjacent to BSS1. In this illustration, assume thatBSS5 is established subsequent to the establishment of BSS1. Varioustechniques for monitoring a BSS, both in the entire bandwidth, as wellas subsets of the bandwidth (in this case a primary 20 MHz channel and asecondary 20 MHz channel) are described further below. In this example,BSS1 will monitor and detect the interference generated by BSS5 and maytake various measures once the interference is detected. For example,BSS1 may opt to lower its bandwidth to 20 MHz and operate in its primarychannel only (illustrated in this example as the portion of channel 420Anot overlapped with BSS5). BSS1 may also attempt to locate an alternateavailable high bandwidth channel 420. It will be clear to one of skillin the art, in light of the teaching herein, that any combination ofhigh and low bandwidth channels may be supported. While, in certaincircumstances, the shared medium may be allocated more efficiently whenthere are no overlapping BSSs, such is not a requirement. Techniquesdescribed further below allow for overlapping high throughput BSSs, aswell as mixed allocations of high and low bandwidth channels, includinginteroperation with legacy channels, for example.

An example set of channel pairings is detailed in Table 1. In thisexample, paired 40 MHz carriers are defined on adjacent carriersnumbered 2 n, 2 n+1, as described above. In this example, the primarycarrier is an even-numbered carrier. Channel numbers defined in IEEE802.11a for FCC U-NII bands are shown as channels in the right columnand are numbered in multiples of 5 MHz (i.e. Channel number 36 indicates5000+36*5 MHz). The 40 MHz carriers are paired as 2 n, 2 n+1 as shown inthe left column.

TABLE 1 Example HT Channel Pairings 40 MHz Carrier Pairs 802.11 ChannelPairs (0, 1) 36, 40 (2, 3) 44, 48 (4, 5) 52, 56 (6, 7) 60, 64 (8, 9)149, 153 (10, 11) 157, 161

FIG. 6 depicts aspects of a wireless communication device, which may beconfigured as an access point 104 or user terminal 106. A wirelesscommunication device is an example STA, suitable for deployment insystem 100. An access point 104 configuration is shown in FIG. 6.Transceiver 610 receives and transmits on connection 110 according tothe physical layer requirements of network 102. Data from or to devicesor applications connected to network 102 are delivered to processor 620.These data may be referred to herein as flows. Flows may have differentcharacteristics and may require different processing based on the typeof application associated with the flow. For example, video or voice maybe characterized as low-latency flows (video generally having higherthroughput requirements than voice). Many data applications are lesssensitive to latency, but may have higher data integrity requirements(i.e., voice may be tolerant of some packet loss, file transfer isgenerally intolerant of packet loss).

Processor 620 may include a Media Access Control (MAC) processing unit(details not shown) that receives flows and processes them fortransmission on the physical layer. Processor 620 may also receivephysical layer data and process the data to form packets for outgoingflows. 802.11 WLAN related control and signaling may also becommunicated between the AP and the UTs. MAC Protocol Data Units (MPDUs)encapsulated in Physical layer (PHY) Protocol Data Units (PPDUs) aredelivered to and received from wireless LAN transceiver 660. An MPDU isalso referred to as a frame. When a single MPDU is encapsulated in asingle PPDU, sometimes the PPDU may be referred to as a frame. Alternateembodiments may employ any conversion technique, and terminology mayvary in alternate embodiments. Feedback corresponding to the various MACIDs may be returned from the physical layer processor 620 for variouspurposes. Feedback may comprise any physical layer information,including supportable rates for channels (including multicast as well asunicast traffic/packets), modulation format, and various otherparameters.

Processor 620 may be a general-purpose microprocessor, a digital signalprocessor (DSP), or a special-purpose processor. Processor 620 may beconnected with special-purpose hardware to assist in various tasks(details not shown). Various applications may be run on externallyconnected processors, such as an externally connected computer or over anetwork connection, may run on an additional processor within wirelesscommunication device 104 or 106 (not shown), or may run on processor 620itself. Processor 620 is shown connected with memory 630, which may beused for storing data as well as instructions for performing the variousprocedures and methods described herein. Those of skill in the art willrecognize that memory 630 may be comprised of one or more memorycomponents of various types, that may be embedded in whole or in partwithin processor 620. In addition to storing instructions and data forperforming functions described herein, memory 630 may also be used forstoring data associated with various queues.

Wireless LAN transceiver 660 may be any type of transceiver. In aspects,wireless LAN transceiver 660 is an OFDM transceiver, which may beoperated with a MIMO or MISO interface. OFDM, MIMO, and MISO are knownto those of skill in the art. Various example OFDM, MIMO and MISOtransceivers are detailed in co-pending U.S. patent application Ser. No.10/650,295, entitled “FREQUENCY-INDEPENDENT SPATIAL-PROCESSING FORWIDEBAND MISO AND MIMO SYSTEMS”, filed Aug. 27, 2003, and assigned tothe assignee of the present application. Alternate embodiments mayinclude SIMO or SISO systems.

Wireless LAN transceiver 660 is shown connected with antennas 670 A-N.Any number of antennas may be supported in various embodiments. Antennas670 may be used to transmit and receive on WLAN 120.

Wireless LAN transceiver 660 may comprise a spatial processor incommunication with each of the one or more antennas 670. The spatialprocessor may process the data for transmission independently for eachantenna or jointly process the received signals on all antennas.Examples of the independent processing may be based on channelestimates, feedback from the UT, channel inversion, or a variety ofother techniques known in the art. The processing is performed using anyof a variety of spatial processing techniques. Various transceivers ofthis type may transmit utilizing beam forming, beam steering,eigen-steering, or other spatial techniques to increase throughput toand from a given user terminal. In aspects, in which OFDM symbols aretransmitted, the spatial processor may comprise sub-spatial processorsfor processing each of the OFDM sub-carriers (also referred to astones), or bins.

In an example system, the AP (or any STA, such as a UT) may have Nantennas, and an example UT may have M antennas. There are thus M×Npaths between the antennas of the AP and the UT. A variety of spatialtechniques for improving throughput using these multiple paths are knownin the art. In a Space Time Transmit Diversity (STTD) system (alsoreferred to herein as “diversity”), transmission data is formatted andencoded and sent across all the antennas as a single stream of data.With M transmit antennas and N receive antennas there may be MIN (M, N)independent channels that may be formed. Spatial multiplexing exploitsthese independent paths and may transmit different data on each of theindependent paths, to increase the transmission rate.

Various techniques are known for learning or adapting to thecharacteristics of the channel between the AP and a UT. Unique pilotsmay be transmitted from each transmit antenna. In this case, the pilotsare received at each receive antenna and measured. Channel stateinformation feedback may then be returned to the transmitting device foruse in transmission. Eigen decomposition of the measured channel matrixmay be performed to determine the channel eigenmodes. An alternatetechnique, to avoid eigen decomposition of the channel matrix at thereceiver, is to use eigen-steering of the pilot and data to simplifyspatial processing at the receiver.

Thus, depending on the current channel conditions, varying data ratesmay be available for transmission to various user terminals throughoutthe system. The wireless LAN transceiver 670 may determine thesupportable rate based on whichever spatial processing is being used forthe physical link between the AP and the UT. This information may be fedback for use in MAC processing.

For illustration purposes, message decoder 640 is deployed betweenwireless LAN transceiver 660 and processor 620. In aspects, the functionof message decoder 640 may be performed within processor 620, wirelessLAN transceiver 660, other circuitry, or a combination thereof. Messagedecoder 640 is suitable for decoding any number of control data orsignaling messages for performing communications within the system. Inone example, message decoder 640 is suitable for receiving and decodinginterference report messages, messages to establish, move or reducebandwidth of a BSS, and others, as described below. Various othermessages may be decoded using any number of message decoding techniqueswell known in the art. Message encoder 650 may be similarly deployedbetween processor 620 and wireless LAN transceiver 660 (and may also beperformed in whole or in part in processor 620, wireless LAN transceiver660, other circuitry, or a combination thereof), and may performencoding of messages such as those just described. Techniques formessage encoding and decoding are well known to those of ordinary skillin the art.

In one embodiment, a Fast Fourier Transform (FFT) (not shown) may beincluded to process a received signal to determine the signals receivedfor each tone in an OFDM scenario. The FFT may be followed by moredecoding and processing to demodulate data on each of the tones. Asdescribed further below, the FFT output may also be used to determinereceived energy of one or more of the tones for use in monitoring thevarious channels. FFT processing at the receiver may also be used forthis purpose even in the case that the transmitted signals are not OFDM.For example, FFT processing permits low complexity implementation offrequency domain equalization for the reception of wideband CDMA signalsas is well known in the art. In aspects, monitoring of the primary andsecondary channels may be desired. Alternate embodiments may includeadditional channels, such as if three or more low bandwidth channelbands are combined to form a high bandwidth channel. These and othermodifications will be clear to those of skill in the art in light of theteaching herein.

In one embodiment, a lower bandwidth channel may comprise a firstplurality of modulation formats, while a higher bandwidth channelcomprises a second plurality of modulation formats, at least one ofwhich is different than the first plurality. For example, a lowerbandwidth OFDM channel may have a first number of tones, while thehigher bandwidth OFDM channel has a greater number of tones. Inalternate embodiment, a lower bandwidth CDMA channel may use a firstchip rate, while a higher bandwidth CDMA channel may use a higher chiprate. Those of skill in the art will readily adapt the teaching hereinto various higher and lower bandwidth channels, where each channel typesupports any number or type of modulation formats.

FIG. 7 depicts aspects of a method 700 for establishing a higherbandwidth channel at one of a subset of lower bandwidth channelboundaries. At 710, a device, such as an access point, determines toestablish a higher bandwidth channel BSS. In this example, there are Nchannels specified of a first bandwidth, an example of which are thetwelve 20 MHz channels 320 described above.

At 720, the access point, or other device, selects an available higherbandwidth channel from M provided channels, the channel boundaries ofthe M channels being a subset of the N channel boundaries. For example,the M channels may be the six 40 MHz channels 420 detailed above.

In one embodiment, an AP or STA attempting to establish an 802.11n BSSor moving to a new carrier conducts Dynamic Frequency Selection (DFS)measurements on all 20 MHz carriers in that band. The AP may use its ownDFS measurements when establishing a new BSS and it may also use DFSmeasurements reported by associated STAs. The algorithm for selectingthe 20 MHz or 40 MHz band to establish a BSS may beimplementation-dependent. If no free 40 MHz band (even-odd pair of 20MHz) is found, the AP attempts to find a free 20 MHz band. If no free 20MHz band can be found, then the AP may establish a BSS with a 20 MHz or40 MHz carrier. This BSS may overlap with another existing BSS. The AP,in this example, should choose a 20 MHz or 40 MHz band that is “leastinterfered” so as to cause minimum disruption to an existing BSS. The APshould use its own DFS measurements when establishing a new BSS, and mayalso use the DFS measurements reported by associated STAs when moving anexisting BSS to a new carrier. The algorithm for selecting a 20 MHz or40 MHz bandwidth to establish a BSS under the non-availability of freecarriers may be implementation-dependent.

At 730, the access point, or other device, establishes the BSS at theselected available channel. In the aspects, a mixed BSS is allowed. AnAP in 40 MHz BSS mode may accept association of 20 MHz only HT STAS, andmay also accept association by 20 MHz legacy 802.11a STAs. In thisexample, all the 20 MHz STAs are supported on the primary carrier. Asdetailed above, for 40 MHz transmissions, the extended Preambleincluding the legacy preamble, legacy SIGNAL field, SIGNAL1 field andextended training fields, are transmitted on both 20 MHz carriers. For20 MHz HT transmissions, the extended Preamble including the legacypreamble, legacy SIGNAL field, SIGNAL1 field and extended trainingfields, are transmitted only on the primary carrier. For legacy 20 MHztransmissions, the Preamble and SIGNAL field are transmitted only on theprimary carrier. NAV protection may be employed on the secondarycarrier. For example, an HT AP (i.e. a 802.11n AP) may attempt tocontinuously reserve the medium in the secondary carrier by setting NAV,either by using the Contention Free Period (CFP) on a Beacon frame, orthrough the use of CTS-to-Self and RTS/CTS on the secondary carrier,techniques known in the art.

A new 40 MHz BSS may be established in the presence of an overlapping 40MHz BSS. If the newly formed 40 MHz BSS is overlapping with an existing40 MHz BSS, then the AP starting the second or subsequent BSS uses thesame primary and secondary carriers as that of the existing 40 MHz BSS.This is ensured by the rule that 40 MHz pairs are of the form 2 n, 2n+1, without requiring any communication between the APs directly orthrough STAs within their respective BSSs, in embodiments subscribing tothis limitation.

A new BSS may also be established in the presence of overlapping anoverlapping 20 MHz BSS. In one embodiment, if establishing a BSS thatmay overlap with an existing 20 MHz HT BSS or a legacy BSS, the APestablishes a 20 MHz BSS (not 40 MHz). In this case, since the paired 20MHz carrier is not free (otherwise there would be no need to establishan overlapping BSS), the paired carrier may be occupied by another 20MHz BSS. Procedures for coordination of medium access in the case of a40 MHz BSS overlapping with different BSSs conducting independent mediumaccess activity on the two 20 MHz carriers may be too complicated andwasteful, and are not supported in aspects. Those of skill in the artwill recognize that reserving a first channel and leaving it dormantwhile waiting for access on a second channel may not optimize resourceutilization. Nonetheless, alternate embodiments may be deployed withoutthis restriction, and additional procedures for attempting to reservebandwidth on both 20 MHz carriers simultaneously (i.e. contending foraccess and reserving access on both) may be deployed.

FIG. 8 depicts aspects of a method 800 for monitoring establishedchannels, measuring interference, and reporting those measurements. Oncea BSS has been established, and one or more STAs are receiving andtransmitting on the channel, in order to maintain the allocation of theshared medium with as little interference as possible, one or more ofthe STAs in a BSS monitor the established channel and may provideassociated feedback. While not mandatory, providing feedback frommultiple STAs within the BSS may provide benefits. For example, a STAlocated within a BSS coverage area may receive and detect interferencefrom a neighboring BSS that is not detectable by another STA in the BSS(such as the access point). Thus, at 810, in this example, each STA in aBSS monitors the established channel.

Monitoring the channel may be different depending on the mode selectedand the BSS type. In the aspects, there will be a primary and secondarychannel forming a 40 MHz higher bandwidth channel, all of which may beused to transmit, or transmission may occur a single 20 MHz channel.Various monitoring techniques are described in further detail below.

At 820, a STA measures interference in the primary and secondarychannels. Again, in various modes, the STA may also measure interferenceon the entire channel, as well. Example measurement embodiments aredetailed further below.

At 830, the STA reports measurements, (or receives measurements fromother STAs in the example case where an access point will make adecision on whether or not to alter the BSS in response to measuredinterference). Example reports are described below. Any messagingtechnique may be used to transmit and receive such measurements.

FIG. 9 depicts aspects of a portion of a STA 104 or 106 used formonitoring an established BSS. In this example, a received signal isdelivered to multiple frequency band energy measurement 910. Energymeasurements 920A-920N are generated for two or more frequency bands,and delivered to interference detector 930. Interference detector 930receives the frequency band energy measurements and makes adetermination of whether interference is detected or not. A mode settingmay be used to identify the context for which interference detectiondecisions are made. Example interference detection embodiments aredetailed further below.

An optional clear channel assessment 940 is shown connected tointerference detector, to indicate that traditional clear channelassessments may be used in conjunction with those described herein. Forexample, clear channel assessment of an idle 40 MHz channel resulting inan indication that the channel is not being used may be sufficient todetermine there is no interference, and multiple frequency band energymeasurement may not be required. On the other hand, since it is possiblefor a lower bandwidth channel to interfere with either the primary orsecondary channel, it may be desirable to detect interference on eitherof those bands in addition to overall interference.

Interference detector 930 accumulates data and/or reports interferencemeasurements. Note that, in aspects, multiple frequency band energymeasurement 910 may be a discrete component, or may be a portion oftransceiver 660, detailed above. Interference detector 930 may becomprised within wireless LAN transceiver 660, or may be included inwhole or in part in processor 620. Those of skill in the art willrecognize that the blocks shown in FIG. 9 are illustrative only. Notethat the energy measurements 920A-920N may correspond to the availablesub-channels of a higher throughput channel, or may be other energymeasurements. Energy measurements 920 may be delivered as aggregates ofvarious sub-bands, or energy measurements for sub-bands may be deliveredto interference detector 930, which may then aggregate the energysub-bands to determine the energy measurements within various channels.

FIG. 10 depicts aspects of multiple frequency band energy measurement910. Those of skill in the art will recognize that various alternatetechniques may be deployed in multiple frequency band energy measurement910. This aspects serves to illustrate the general principals describedherein for interference detecting on multiple frequency band wirelessnetworks, and is particularly well suited for the example OFDM wirelessLAN described above or other systems where the receivers use frequencydomain processing of the received signals. In this example, the receivesignal is delivered to a Fast Fourier Transform (FFT) 1010. Various FFTtechniques are well known in the art, and any FFT may be deployed in agiven embodiment. When used in the OFDM context, FFT 1010 will produceenergy measurements 1020A-N for the various OFDM tones or bins. Theseenergy measurements are delivered to energy calculator 1030, which mayaccumulate the energy for a particular bin or tone or may aggregateenergy for a group of tones. This method may also be used with receptionof non-OFDM transmissions to obtain the received energy in the group oftones, although the tones are not directly modulated with transmitsymbols as in OFDM.

In one example, using a contiguous high throughput channel, as describedabove, the FFT will produce a plurality of tones. Half of those toneswill correspond to the primary channel, and half will correspond to thesecondary channel. Thus, energy calculator 1030 may accumulate theenergy for the primary channel tones to produce an energy measurementfor the primary channel. Similarly, energy calculator 1030 may aggregatethe energy for the tones corresponding to the secondary channel toproduce a secondary energy measurement.

In alternate embodiments, where the wider channel is not necessarilycontiguous, those of skill in the art will recognize that a higher orderFFT 1010 may be used to pull out a greater number of tones correspondingto the overall bandwidth in which any portion of the channel may belocated. In similar fashion, energy calculator 1030 may select the tonescorresponding to the primary and secondary channels (or additionalchannels, in alternate embodiments), and generate an energy measurementfor each frequency band within the multiple frequency band wirelessnetwork.

FIG. 11 depicts aspects of a method 1100 for modifying a BSS in responseto measured interference. A similar method may also be used fordetermining an initial channel for establishing a BSS, as describedabove. Several procedures are detailed in FIG. 11. These procedures areexamples only, as various embodiments may employ any one or more ofthem, and these procedures may also be combined with various othertechniques disclosed herein.

At 1110, using any measuring or monitoring techniques, such as thosedetailed herein, an access point (or other station responsible forallocating a BSS frequency and/or bandwidth) measures the primary and/orsecondary channel. Alternatively, or additionally, this STA may receivesimilar measurements from other STAs in the BSS. At 1120, if nointerference is detected, the process returns to 1110, where monitoringmay continue. If interference is detected, then the STA may attempt tolocate another high bandwidth channel at another location, as shown at1130. In one embodiment, the STA may look for an unoccupied highbandwidth channel. In another embodiment, the allowing for someinterference on the high bandwidth channel, the STA looks for a channelwith lower interference than that detected at 1120. If such a channel islocated, proceed to 1140 where the STA relocates the BSS to theavailable high bandwidth channel. Those of skill in the art willrecognize various techniques for signaling or messaging to the STAsassociated with the BSS that a modification to the channel assignmentwill be made. Then the process may return to 1110 to continue monitoringat the new high bandwidth channel.

If, at 1130, another high bandwidth channel is not available, at 1150,use available measurements on lower bandwidth channels or obtain suchmeasurements from STAs. At 1160, drop back to a lower bandwidth channel.In the aspects, this entails reducing from a 40 MHz channel to a 20 MHzchannel. The BSS may be relocated to either the primary or secondarychannel, depending on the type of interference detected. Once the BSShas been relocated and operating on the lower bandwidth channel, then,at 1170, determine if interference is still detected on that channel. Ifinterference is detected, the process reverts to 1150 and then 1160 toobtain measurements and relocate the BSS to an alternate available lowbandwidth channel, if one is available.

If, at 1170, there is no further interference detected, the process maystop. Note that a method 1100 may be iterated indefinitely to continuemonitoring the channels on which the BSS operates. This allows a higherbandwidth capable access point and STAs to continue monitoring highbandwidth channels even while the BSS is operating on a low bandwidthchannel and to relocate to a high bandwidth channel when one becomesavailable.

FIG. 12 depicts aspects of a method 1200 for determining if interferenceis occurring on a multiple frequency band wireless network. The variousembodiments detailed herein have been described in a Carrier SenseMultiple Access/Collision Avoidance (CSMA/CA) context. In other words,each STA listens to the shared medium before transmitting. Thus, eachSTA must be able to determine if the channel is free before attemptingto transmit.

Because the multiple frequency band WLAN is occupying more than oneband, and other STAs such as a legacy BSS may begin to transmit oneither the primary or secondary channels, the STAs supporting the highbandwidth network need to be able to monitor both the primary andsecondary channels (as well as additional channels, if supported). Whileit is possible to deploy two full receive chains to dedicate tomonitoring both the primary and secondary channel, for example in 20 MHzmode, that may be prohibitively expensive for a given embodiment. Asdetailed herein, and described above with respect to FIGS. 9 and 10, itis not necessary to deploy a full receive chain on both channels todetermine whether or not there is interference. The method 1200 detailedin FIG. 12 may be used with an embodiment such as shown in FIG. 9 orFIG. 10, as well as any other means for detecting interference on thevarious channels known in the art.

Several example modes are illustrated in FIG. 12. In one example, thechannel (whether high or low bandwidth) is idle and the STA monitoringthat channel is able to receive and monitor, expecting to find thechannel idle. In another example, the channel is active, in a mixed BSSmode (i.e. one or more STAs in the BSS operate at a lower bandwidth thana maximum supported by the BSS, such as a 20 MHz transmission within a40 MHz bandwidth channel). A third example is when a transmission isactive using a high bandwidth channel (i.e. a 40 MHz transmission in theaspects).

In describing the method of FIG. 1200, the aspects 20 and 40 MHzchannels will be used. Those of skill in the art will recognize that anysize channels may be deployed for relatively lower and relatively higherbandwidth systems, as well as channels additional to the primary andsecondary. At 1210, if the channel is idle, and the monitoring STA is inreceive mode, proceed to 1215. At 1215, a Clear Channel Assessment (CCA)of the entire 40 MHz channel, or the 20 MHz channel if in 20 MHz receivemode, is performed. In this example, the entire channel is expected tobe idle, so any energy detected (above a threshold, for example), asindicated at 1220, may be used to determine there has been interference.If energy is detected, then an interference report may be generated orinterference event statistics may be updated at 1225 and the process maystop. Various example interference reports are detailed below. If noenergy is detected during the clear channel assessment, then there is nointerference detected at 1230, and the process may stop.

If, at 1210, the channel is not idle, then, at 1240, determine if thereis a 20 MHz transmission on a first channel (such as the primarychannel, for example). If so, measure the energy in the second channelat 1245. Note that, before any transmission, a clear channel assessmentmust be made for the 20 MHz transmission on the first channel. Again, asdescribed above, an entire receive chain is not required to measure theenergy in a second channel, even while receiving on the first channel.For example, in a receiver using frequency domain processing, an FFT maybe deployed to measure energy at the various tones. When 20 MHZtransmissions is being used, the energy of the tones not used in that 20MHZ transmission may be measured. At 1250, if energy is detected on thesecond channel, then interference on the second channel has beendetected. At 1255, an interference report may be generated orinterference event statistics may be updated or other appropriate actiontaken. If energy is not detected on the second channel, then, as before,proceed to 1230. At 1230, no interference has been detected and theprocess may stop.

If the channel is not in idle mode and the transmission is not a 20 MHztransmission, then, if a 40 MHz transmission is to transpire, at 1270,proceed to 1275. At 1275, measure energy in both bands. In this example,the three conditions to be tested have been illustrated, and the processproceeds to 1270 to stop if this is not a 40 MHz transmission. In analternate embodiment additional scenarios may be tested in alternateembodiments. At 1280, an energy difference is computed between themeasured energy from both bands. If the energy difference meets certaincriteria (exceeding a threshold, for example) then interference isreported at 1285. If not, the process may stop. Measuring an energydifference between the two bands (or additional bands, in an alternateembodiment) is a useful when the 40 MHz transmission is conducted usingapproximately the same energy across the available bandwidth. Then, ifan alternate BSS is interfering on either the primary or the secondarychannel, then the additional energy would be measured on the respectivechannel. In this case, there would then be a detected energy differencebetween the two bands.

Note that the interference report generated at 1225, 1255 or 1285 may beused to generate a report for transmission to a remote STA for use inmodifying the BSS, or alternate steps may take place. For example,various counters tabulating interference types may be incremented,and/or a report generated, when certain criteria (such as exceeding athreshold) are met. Alternately, the various reports may be identicaland a single report of interference or not interference may be made.

FIG. 13 depicts aspects of a method 1300 for responding to BSSmodification messages from an alternate BSS. In this example, at 1310, aSTA monitors messages from another BSS. For example, interference mayhave been detected. Or, the alternate BSS may be using a communicationprotocol that is decodable by the STA employing the method. The STA maydecode messages directed to STAs in the alternate BSS, and may makedecisions for maintaining its BSS accordingly. At 1320, if the other BSSsignals a switch to a lower bandwidth channel (such as the primary orsecondary channel), perhaps due to interference detection at that BSS,proceed to 1330. If no such message is received, the process returns to1310 and monitoring may continue. If such a message or signal isdetected in an alternate BSS, then the access point (or other devicecapable of signaling a BSS change) may signal to the current BSS toswitch to an alternate low bandwidth channel, at 1330. The alternate lowbandwidth channel selected would most conveniently be a channel notselected by the other BSS from which the signal was received. Forexample, if a signal from the alternate BSS to STAs within that BSS isto switch to the secondary channel, then the current BSS may switch tothe primary channel, and vice versa. In some instances, if both BSSsmeasure interference at the same time and send messages to theirrespective STAs to switch to the primary or secondary channel at thesame time, then both BSSs may switch to the same lower bandwidthchannel. In such a case, both BSSs would again detect interference.Additional back-off schemes may be deployed in such circumstances toavoid such a situation, or other techniques may be deployed. In duecourse, the likelihood is that both BSSs, perhaps following a methodsuch as described above with respect to FIG. 11, would locate alternatechannels on which to communicate without interference.

Aspects illustrating various monitoring and BSS frequency modificationtechniques is described below. Example report types are also described.Those of skill in the art will recognize myriad variations in light ofthe teaching herein. In a 40 MHz BSS STAs access the medium usingCSMA/CA procedures on the primary carrier. If interference on thesecondary carrier is detected during back-off, the STA should transmiton the primary carrier only.

During back-off, as well as during any 20 MHz reception on the primarycarrier in the 40 MHz BSS, 40 MHz capable STAs that are awake performCCA on the secondary carrier. When interference is detected on thesecondary carrier or when a preamble is detected on the secondarycarrier, the STA increments a Secondary Carrier Interference Event(SCIE) counter.

Alternately, each STA may maintain and report multiple interferenceevent counters for each possible interference event type. Examplesinclude: (i) Detected preambles, (ii) Detected frames with a differentSSID, (iii) Detected noise level above a threshold, or (iv) Detectedinterference from other sources.

SNR degradation may be measured on the secondary carrier. Duringreception of 40 MHz transmissions, STAs may compute the difference inSNR between the primary and secondary carriers, as described above. Theincreased interference on the secondary carrier may come from a 20 MHz(or legacy) BSS that may not be capable of DFS. If the differenceexceeds a threshold, the STA increments the appropriate SCIE counter.

SCIE reports may be generated. In an example infrastructure BSS, STAsmay autonomously, or on request from the AP, report the SCIE Countervalue (or multiple SCIE counter values for the various interferencetypes). The SCIE Counter is reset once the AP acknowledges the report.The AP action on the receipt of SCIE Reports may beimplementation-dependent, examples are detailed above. The AP shouldtransition the BSS to 20 MHz operation if the SCIE counts are excessive(or find an alternate high bandwidth channel). A transition to 20 MHzmay be announced by the STA transmitting the Beacon.

When excessive SCIE counts are present (whether measured, reported, orboth), the AP stops use of the secondary carrier. The AP may requestother STAs in the BSS to make additional measurements. The AP may moveto another 40 MHz carrier or transition to 20 MHz operation on theprimary carrier and terminate use of the secondary carrier, as describedabove.

A mandatory switch to 20 MHz may be deployed in some embodiments, usingtechniques similar to that shown in FIG. 13. In a 40 MHz overlappingBSS, when the AP observes that the SCIE Counts are low, and there isexcessive activity from an overlapping BSS on the primary carrier, theAP may transition the BSS to 20 MHz operation on the secondary carrier.An AP (in another 40 MHz BSS) that receives a Beacon from theoverlapping BSS, announcing the transition to 20 MHz operation on thesecondary carrier, transitions to 20 MHz operation on the primarycarrier and indicates this information in subsequent beacons using802.11b mechanisms.

Multiple overlapping BSSs may be supported. When multiple overlappingBSSs are present, DFS procedures may be deployed to gain access to thechannel. In some cases, the result will be overlapping 20 MHz BSS as inexisting 802.11.

Detailed below are example procedures for establishing 40/20 MHz BSS ina new band, or relocating to another new band. A transceiver may bedeployed in accordance with the following requirements.

The transceiver will transmit on the primary channel if the secondary isbusy. During 40 MHz operation, the transceiver conducts clear channelassessment (CCA) on both 20 MHz carriers, as described above. It followsmedium access rules on the primary 20 MHz carrier. When the STAdetermines that it has permission to access the medium according to theCSMA/CA rules on the primary channel, and if the STA determines that themedium is busy on the secondary channel, the STA transmits on the 20 MHzprimary carrier only.

For 40 MHz transmissions, the preamble and legacy SIGNAL are transmittedon both carriers. The SIGNAL field indicates whether the MIMO trainingand data are transmitted on 40 MHz or on the 20 MHz primary carrieronly.

Reception may be made on both the primary and secondary channels, or theprimary only. In a 40 MHz BSS, a 40 MHz transceiver listens for CCA onboth carriers. The receiver is able to detect a preamble and decode thelegacy signal field either on the primary carrier or on both carriers.When CCA declares detected energy on the medium, the receiver is able totest all of the following hypotheses: (i) signal (preamble) on primary,idle on secondary; (ii) signal on the primary and secondary; and (iii)signal on primary and interference on the secondary. Depending on theresult of these measurements, as well as indication in the SIGNAL field,the receiver is capable of decoding a 20 MHz transmission on the primarycarrier, or a 40 MHz transmission spanning the two carriers.

As described above, during reception on the secondary carrier when themedium is idle, when there is a 20 MHz transmission on the primary, orwhen there is a 40 MHz transmission on both carriers, the receiver isable to detect interference on the secondary carrier. A number ofmethods may be used to detect interference on the secondary carrier (forexample, as described above with respect to FIG. 12). When the medium isidle, the STA may detect the presence of transmission from another BSS(indicated by the presence of a different SSID in the MAC header of thetransmission). When the medium is busy with a 20 MHz transmission,energy detected on the secondary carrier indicates interference. Whenthe medium is busy with a 40 MHz transmission, a STA may determine anSNR metric that indicates a difference in SNR on the two carriers. TheSTA collects and reports these information events as detailed above.

Examples of permitted carriers in overlapping BSSs with 40 MHz operationfor this aspects are detailed in Table 2. Note that permitted andnon-permitted overlapping BSS scenarios are specific to this embodiment.As described above, alternate embodiments may allow or disallow anycombination of various overlap types.

TABLE 2 Examples of Permitted Carriers in Overlapping BSS with 40 MHzOperation Overlapping Overlapping Overlapping BSS 1 BSS 2 BSS 3Permitted Comment 40 MHz: 40 MHz: Not present Yes Overlapping 40 MHzBSS. 2n, 2n + 1 2n, 2n + 1 Either BSS may announce a switch to 20 MHz.The other one must then switch to other 20 MHz carrier. 40 MHz: 40 MHz:Not present No 40 MHz carriers must be of 2n, 2n + 1 2n + 1, 2n + 2 theform 2n, 2n + 1 40 MHz: 20 MHz: Not present Yes Overlap with 20 MHz on2n, 2n + 1 2n Primary carrier. 40 MHz: 20 MHz: Not present No BSS 1 mustswitch to 20 2n, 2n + 1 2n + 1 MHz operation on either 2n or 2n + 1. Orfind an alternate 40 MHz carrier. 40 MHz: 20 MHz: 20 MHz: No BSS 1 mustswitch to 20 2n, 2n + 1 2n 2n + 1 MHz operation on either 2n or 2n + 1.Or find an alternate 40 MHz carrier. 40 MHz: 20 MHz: 20 MHz: Yes Overlapwith 20 MHz on 2n, 2n + 1 2n 2n Primary carrier.

The following are several additional examples of techniques that may beused when detecting Secondary Carrier Interference Events. If, duringCCA on the primary, there is a transmission on the secondary, it must beinterference. In one embodiment, there is no need to decode the BSS ID.During reception of a 40 MHz transmission, if there is a lower SNR onthe secondary, then it may be concluded to be interference. If, during a20 MHz transmission, there is energy on the secondary, then it must beinterference. In these instances, therefore, it is not necessary todecode the BSS ID from transmissions on the secondary to determine thatthere is interference on the secondary carrier. This is useful when, forexample, there is energy on the secondary carrier, and the data rate andsteering may be such that the interfered STA is unable to decode the MACheader of the interfering transmission.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentdisclosure. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the disclosure. Thus, the present disclosure is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. An apparatus comprising: a receiver configured toreceive a signal on a shared channel comprising at least a primarychannel and a secondary channel; an energy calculator configured tocalculate an energy measurement of a plurality of tones of the primarychannel and an energy measurement of a plurality of tones of thesecondary channel and to compute an energy difference between the energymeasurement of the primary channel and the energy measurement of thesecondary channel, wherein calculating the energy measurement of theplurality of tones of the primary channel comprises aggregating theenergy of the plurality of tones of the primary channel and whereincalculating the energy measurement of the plurality of tones of thesecondary channel comprises aggregating the energy of the plurality oftones of the secondary channel; and a processor configured to detectinterference in response to the energy measurement of the primarychannel and the energy measurement of the secondary channel, whereindetecting interference comprises determining interference in a secondmode, in which transmission is expected on the primary channel and thesecondary channel, when the computed energy difference is above anenergy difference threshold.
 2. The apparatus of claim 1, furthercomprising an FFT with an input and an output, the input configured toreceive the received signal, and the output coupled to the energycalculator.
 3. The apparatus of claim 1, further comprising a messageencoder for generating an interference report message in response todetected interference.
 4. An apparatus, operable with a shared channelcomprising at least a primary channel and a secondary channel,comprising: means for measuring energy of a plurality of tones of theprimary channel, wherein measuring the energy of the plurality of tonesof the primary channel comprises aggregating the energy of the pluralityof tones of the primary channel; means for measuring energy of aplurality of tones of the secondary channel, wherein measuring theenergy of the plurality of tones of the secondary channel comprisesaggregating the energy of the plurality of tones of the secondarychannel; means for computing an energy difference between the measuredenergy of the primary channel and the measured energy of the secondarychannel; and means for determining interference in accordance with themeasured energy of the primary channel and the measured energy of thesecondary channel, wherein the means for determining interferencecomprises means for determining interference in a second mode, in whichtransmission is expected on the primary channel and the secondarychannel, when the computed energy difference is above an energydifference threshold.
 5. In a Carrier Sense Multiple Access/CollisionAvoidance system, supporting transmission on a shared channel comprisingat least a primary channel and a secondary channel, a method comprising:measuring energy of a plurality of tones of the primary channel, whereinmeasuring the energy of the plurality of tones of the primary channelcomprises aggregating the energy of the plurality of tones of theprimary channel; measuring energy of a plurality of tones of thesecondary channel, wherein measuring the energy of the plurality oftones of the secondary channel comprises aggregating the energy of theplurality of tones of the secondary channel; computing an energydifference between the measured energy of the primary channel and themeasured energy of the secondary channel; and determining interferencein accordance with the measured energy of the primary channel and themeasured energy of the secondary channel, wherein determininginterference comprises determining interference in a second mode, inwhich transmission is expected on the primary channel and the secondarychannel, when the computed energy difference is above an energydifference threshold.
 6. The method of claim 5, further comprising:performing a Fast Fourier Transform (FFT) of the shared channel toproduce a plurality of energy measurements for a corresponding pluralityof tones; and wherein: the energy of the primary channel is measured inaccordance with a first subset of the plurality of energy measurements;and the energy of the secondary channel is measured in accordance with asecond subset of the plurality of energy measurements.
 7. The method ofclaim 5, wherein determining interference comprises determininginterference in a first mode, in which transmission is expected on theprimary channel only, when the measured energy of the secondary channelis above a secondary channel energy threshold.
 8. The method of claim 5,wherein determining interference comprises determining interference in athird mode, in which no transmission is expected on the primary channelor secondary channel, when either the measured energy of the primarychannel or the measured energy of the secondary channel is above an idlechannel energy threshold.
 9. The method of claim 5, further comprisingincrementing an interference counter value when interference isdetermined.
 10. The method of claim 5, further comprising generating aninterference report message in accordance with determined interference.11. The method of claim 5, further comprising modifying a channelparameter when determined interference meets predefined criteria. 12.The method of claim 11, wherein modifying a channel parameter comprisesreducing the bandwidth of the channel to the bandwidth of the primarychannel.
 13. The method of claim 11, wherein modifying a channelparameter comprises reducing the bandwidth of the channel to thebandwidth of the secondary channel.
 14. The method of claim 11, whereinmodifying a channel parameter comprises changing a frequency carrier ofthe channel.